1. Field of the Invention
The present invention relates to a deflection yoke used for a cathode ray tube included in a television, a computer monitor and the like, and more particularly relates to a shape of a deflecting coil.
2. Related Background Art
FIG. 11 is a side view of a cathode ray tube device including a cathode ray tube and a deflection yoke, with an upper portion thereof broken away for clarity. The cathode ray tube 8 includes a glass bulb 3 and an electron gun 7 provided in a neck 4, where the glass bulb 3 further includes a display screen (phosphor screen) 2 inside of a front panel 1 and the electron gun 7 emits an electron beam 6 onto the display screen 2 through a shadow mask 5. A deflection yoke 9 is installed on a so-called cone unit of the cathode ray tube 8.
The deflection yoke 9 is assembled so that a horizontal deflecting coil 11 is located at the innermost position to contact with the cathode ray tube, and a separator 12, a vertical deflecting coil 13 and a core 14 are overlaid on the horizontal deflection coil 11 in the stated order. The separator 12 functions so as to insulate the horizontal deflecting coil 11 from the vertical deflecting coil 13 and fix them.
The horizontal deflecting coil and the vertical deflecting coil are saddle-type coils, and are each made up of a bend portion at a side of the front panel 1 (hereafter referred to as a xe2x80x9cscreen side bend portionxe2x80x9d); a bend portion at a side of the electron gun 7 (hereafter referred to as a xe2x80x9cneck side bend portionxe2x80x9d); and a cone portion that connects the screen side bend portion and the neck side bend portion. Note here that the bend portion also is referred to as an arc portion.
FIG. 12 shows one of a pair of the vertical deflecting coils 13, as viewed from the screen side. The lateral axis in this figure corresponds to the X axis, the vertical axis corresponds to the Y axis, and the Z axis not illustrated in this drawing corresponds to the tube axis. In the deflection yoke having such a saddle-type vertical deflecting coil 13, the screen side bend portion 15 of the vertical deflecting coil 13 is approximately in the form of a segment of a circle, as shown in FIG. 12.
FIG. 13A shows the distortion of scanning lines on the screen, which is formed by the electron beam deflected by a deflection yoke that generates a normal self-convergence magnetic field. This distortion is called a xe2x80x9craster distortionxe2x80x9d. A lateral distortion as shown in FIG. 13A, resembling a bobbin, is called a xe2x80x9clateral (i.e., right and left) pincushion distortionxe2x80x9d 16 and a distortion generated inside of the lateral pincushion distortion 16 is called a xe2x80x9clateral (i.e., right and left) inner pincushion distortionxe2x80x9d 17.
Conventionally, well-known technology for correcting the lateral pincushion distortion 16 includes a method making use of a lateral pincushion distortion correction circuit that uses a configuration employing a pincushion transformer and for modulating a power supply voltage of a horizontal deflecting circuit in a TV set or a computer monitor set. These technologies are, for example, disclosed in JP6(1994)-315094 A and JP9(1997)-181931 A.
FIG. 13B illustrates a lateral inner pincushion distortion 18, which remains after the correction of a lateral pincushion distortion by means of the conventional lateral pincushion distortion correction circuit. Conventionally, methods for correcting such a lateral inner pincushion distortion 18 are, for example, as follows: that is, JP 9(1997)-149283 A discloses a technology of providing a correction coil in the deflection yoke. The correction coil provided is a reactor coil activated by a flow of a horizontal and vertical deflecting currents; and JP 7(1995)-39163 U discloses a technology of installing four magnets, two magnets of which installed along each of the X axis and the Y axis of the large-diameter side (i.e., screen side) of the deflection yoke.
However, according to the correction method disclosed in JP 7(1995)-39163 U, the magnets are added newly so as to correct the lateral inner pincushion distortion, which increases the number of components so that the structure would be complicated and also increases the number of assembling processes. Furthermore, if an error occurs during installation of the magnets, this error would cause a variation in the correction capability, which leads to a problem of a variation in the degree of a distortion of the displayed image. According to the correction method disclosed in JP 9(1997)-149283 A, the correction coil is added newly and the horizontal and vertical deflecting currents are used for the current supply of the coil, which would cause a problem of an increase in the deflecting power.
Also, since color cathode ray tubes used for the recent TVs and computer monitors are required to have a flatter screen and save space, the cathode ray tubes with a wider deflection angle have been developed. As a result, the deflection aberration is increased, so that the increase in the lateral inner pincushion distortion becomes a problem.
Therefore, with the foregoing in mind, it is an object of the present invention to provide a deflection yoke having the capability of correcting a lateral inner pincushion distortion in a simple configuration with a magnetic field generated by a deflecting coil itself, without adding a component for compensating the distortion and increasing a deflecting power.
To fulfill the above-stated object, a first deflection yoke according to the present invention, which is installed on a cathode ray tube, includes a saddle-type vertical deflecting coil including a screen side bend portion, a neck side bend portion and a cone portion connecting the screen side bend portion and the neck side bend portion. When viewing the screen side bend portion of the vertical deflecting coil from a screen side of the cathode ray tube in a direction along a tube axis, the screen side bend portion includes portions located on either side across an axis passing through the tube axis and extending along a diagonal direction of a screen and having a distance from the tube axis longer than a distance at a portion in the diagonal direction of the screen from the tube axis.
Next, a second deflection yoke according to the present invention, which is installed to a cathode ray tube, includes a saddle-type vertical deflecting coil including a screen side bend portion, a neck side bend portion and a cone portion connecting the screen side bend portion and the neck side bend portion. When viewing the screen side bend portion of the vertical deflecting coil from a screen side of the cathode ray tube in a direction along the tube axis, a distance from the tube axis is the minimum at a portion close to a diagonal direction of the screen of the screen side bend portion.